Mars orbiter spots rover on weird plateau

Imagery could help scientists figure out history of ‘Home Plate’

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An image taken by NASA's Mars Reconnaissance Orbiter shows the Red Planet rock formation known as Home Plate, with a black circle added to highlight the location of NASA's Spirit rover. Click on the image for a larger version.

Such imagery could provide new clues about the plateau's geological history — and serve as a guide for Spirit's future sojourns around Home Plate, Ken Herkenhoff of the U.S. Geological Survey told msnbc.com on Monday.

"It's just cool to see the rover from orbit, but it is also very useful for operations," said Herkenhoff, who is on the science team for NASA's twin Mars rovers as well as for the Mars Reconnaissance Orbiter, or MRO.

The color image of Spirit on Home Plate was taken on Sept. 27 by the Mars Reconnaissance Orbiter's High Resolution Imaging Science Experiment, better known as the HiRISE camera. At the time, the spacecraft was flying about 168 miles (270 kilometers) above the surface.

This isn't the first time the orbiter has spotted one of NASA's rovers. Last year, HiRISE traced Spirit's tracks through Gusev Crater and watched its twin, the Opportunity rover, as it made its way around the rim of Victoria Crater. It has also taken pictures of the two Viking landers that set down on Mars in 1976.

The resolution of the image released Monday is not good enough to see Spirit as anything more than a dot on the rock. One pixel element represents about 32 inches or 81 centimeters. Nevertheless, the picture provides important confirmation from above for what Spirit is seeing on the ground, Herkenhoff said.

"I really recognize how useful the HiRISE data are in our planning and our interpretation of the MER [Mars Exploration Rover] data," he said.

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The colors in the image, created by combining the camera's blue-green and red channels, are particularly valuable. So far, the orbital imagery confirms the prevailing view that Home Plate was created ages ago as an
explosive volcanic deposit
, Herkenhoff said.

HiRISE's image hints that the deposits might be more widespread than scientists originally thought, he said. "There are similar features and formations with similar color elsewhere in the HiRISE image, so that does help constrain the interpretation," he said.

It's not exactly surprising that the color variations in the HiRISE image correlate with Spirit's imagery. "It's more comforting that we seem to have gotten that right," Herkenhoff said. "But it's still puzzling [to consider] what's causing those variations."

The variations might be due to the way Home Plate and the other features have been eroded by wind over millions of years, or perhaps they're caused by coatings that have been overlaid on the rock, he said.

Since the HiRISE picture was taken, Spirit has been roaming around in search of a safe place to spend the next Martian winter. At first, Spirit headed south toward a potential "off-ramp" that would lead away from Home Plate. However, the mission team at NASA's Jet Propulsion Laboratory decided instead to send Spirit northward, to a spot where the solar-powered robot could soak up more of the sun's rays to get it through the winter.

The Opportunity rover, meanwhile, is parked at what mission managers call a "bathtub ring" of rock layers just below Victoria Crater's rim. The rover is focusing on a rock layer nicknamed Smith — and coping with a bent brush on its rock abrasion tool, according to a status report released last week.

The two rovers are both in good condition almost four Earth years since they landed on the Red Planet — which has come as a pleasant surprise for mission managers who originally planned for a 90-day primary mission. MRO arrived at the Red Planet in March 2006 for what's expected to be a four-year, $720 million primary mission.